Monofilament for use in screen gauze and screen gauze using the same

ABSTRACT

A screen gauze formed of a core-sheath composite monofilament comprising the core  1  formed by a fiber-forming polymer  4  containing a material  3  having a property of absorbing light at wavelengths of 350 nm to 450 nm and the sheath  2  formed by a fiber-forming polymer  5,  the core-sheath composite monofilament having average reflectance of 15% or less to light at wavelengths of 350 nm to 450 nm, and a screen gauze using the same. The monofilament is free from strength reduction, scum generation and abrasion of related parts such as reed, and makes no difficulty in ink-release, and requires no dyeing process and thus no additional cost therefor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 11/569,903, filed on Dec. 1, 2006, which is a 371 of International Application No. PCT/JP2005/009732, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2004-165930 filed Jun. 3, 2004, and Japanese Patent Application No. PCT/JP2004/014185 filed Sep. 28, 2004 the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a monofilament for use in a screen gauze and a screen gauze using the same monofilament.

BACKGROUND OF THE INVENTION

As a screen gauze for forming a printing pattern in screen printing, has been generally used a woven fabric such as a plain weave fabric or a twill weave fabric obtained by weaving monofilaments made of fiber-forming polymers such as polyester or polyamide.

The screen gauze is, for example, printed by the following method. After a gauze fabric obtained by weaving monofilaments is stretched over a frame, a photosensitive resin is coated on such a stretched fabric and is dried for forming a photosensitive film. Then, a positive film is adhered on a surface of the photosensitive film and is exposed to ultraviolet rays. Such exposed portions cause photochemical reaction so as to change into water-insoluble. Unreacted photosensitive film corresponding to opaque portions of the positive film is rinsed off with water so that screen corresponding thereto is exposed (developed). When placing the thus obtained screen on an object to be printed and pouring ink thereon, the ink is forced out of texture of the screen for printing. In this method, it is important to prevent halation at the time of exposure to ultraviolet rays. Since halation occurs on a surface of the fabric yarn at the time of exposure to ultraviolet rays, undesired portions as well as desired portions are exposed to light and are cured, so that printing accuracy drastically deteriorates.

To prevent halation, relatively large amounts of titanium oxide has conventionally been blended into the monofilament for forming the screen gauze so as to irregularly reflect light at the time of exposure by means of the titanium oxide as much as possible. However, there is the problem that halation cannot be completely prevented because light reflection cannot be sufficiently restricted in visible light range even if the monofilament containing titanium oxide is used.

Further, since a surface of the monofilament containing titanium oxide becomes uneven because of protrusion of titanium oxide particles, there are problems such as unclear printing because of difficult ink-release in printing, or poor working efficiency by scams or the like formed by the scraping of blades of a reed during weaving.

As a screen gauze containing a minimized amount of titanium oxide, has been proposed a screen gauze using a monofilament containing ultraviolet absorber and a yellowish pigment or a reddish pigment (see a microfilm copy of Utility Patent Application No. S60-119078 (Unexamined Utility Patent Publication No. S62-28567)) or a screen gauze using a core-sheath composite monofilament in which only the sheath portion is colored or dyed so that light-absorbing property is imparted (see Unexamined Patent Publication No. S64-47591).

Further, a method of coating a film for physically preventing ultraviolet rays from reflecting at warps and wefts of a screen gauze is proposed by Unexamined Patent Publication No. 2003-19875.

However, since ultraviolet absorber and pigments are dispersed and contained in the whole monofilament of the screen gauze according to Utility Patent Publication No. S62-28567, there is the problem that the monofilament deteriorates in its filament strength and tends to easily cause troubles in weaving.

Further, since some unevenness is caused on a surface of the monofilament, which is caused at lower frequency than in the conventional monofilament containing a high percentage of titanium oxide, there still remains the problems that trouble in weaving and trouble in printing such as difficult ink-release cannot be completely eradicated.

In the case where the monofilament is obtained by kneading ultraviolet absorber, a pigment and the like into the sheath ingredient, according to Patent Publication No. S64-47591, there even still remains the problem easily caused by unevenness formed on a surface of the monofilament by particles of pigments or the like. For example, when pigments or the like are contained in the sheath ingredient, so-called “uneven yarn” such as variation in degree of fineness, physical properties or the like are caused, which tend to cause abnormal of print, resulting in deteriorated accuracy. Especially, if a large amount of a pigment is kneaded into the sheath to sufficiently prevent halation, spinning workability deteriorates and also it easily causes troubles in weaving such as scams or the like formed by the scraping of blades of a reed in weaving a high mesh screen gauze. Further, Patent Publication No. S64-47591 describes that a pigment or the like is imparted to the woven screen gauze by means of a dyeing process, which means that additional process for dyeing is required and there is the problem of increased manufacturing cost. Still further, in the case where a core-sheath structure is formed by using polymers in combination of, for example, polyester and nylon 6, which are different in heat shrinkage rate, there is the problem that physical properties such as the strength of the monofilaments deteriorate due to dyeing, resulting in difficulty in stretching the screen gauze.

In the method according to Unexamined Patent Publication No. 2003-19875 where the warps and wefts of the screen gauze are covered with an ultraviolet antireflection film, additional process is required and special equipment is required, resulting in increased manufacturing cost.

The present invention has been made to solve these problems, and has an object to provide an excellent monofilament free from strength reduction, scum generation and abrasion of related parts such as reed, which makes no difficulty in ink-release, and requires no dyeing process and no special equipment, and thus no additional cost therefor, and a screen gauze using the monofilament.

DISCLOSURE OF THE INVENTION

The above-described object of this invention can be attained by a core-sheath composite polyester monofilament for use in a screen gauze, characterized in that the core contains a material having a property of absorbing light at wavelengths of 350 nm to 450 nm and the core-sheath composite polyester monofilament has average reflectance of 15% or less to light at wavelengths of 350 nm to 450 nm. Therefore, when a screen gauze is formed by using such a core-sheath composite polyester monofilament, halation does not occur and thus clear printing pattern can be obtained. Since light absorbing material is contained in the core ingredient, scum generation and abrasion of related parts such as reed can be restricted and thus a high density screen gauze of 300 mesh or more can stably be woven. Further, the dyeing process and special equipment are not required, resulting in an advantage that no additional cost is incurred.

Especially, among the core-sheath composite monofilament of the present invention, when the light-absorbing material is present in an amount of 0.1 to 2.0% by weight based on the total core, thus obtained monofilament has more sufficient filament strength, and keeps an excellent halation-preventive effect, and also brings about stable and good spinning workability.

Especially, when the cross-sectional area ratio of core to sheath of the monofilament is in a range of 40:60 to 90:10, thus obtained monofilament keeps an excellent halation-preventive effect, and has more sufficient filament strength because the sheath fulfills a role of protecting the core, and thus can endure harsh abrasion in the weaving of the high mesh screen or printing.

Especially, when the core-sheath composite monofilament has the elongation at break of 20 to 30% and the strength at break of 5.5 cN/dtex or more, the resultant screen gauze can be stretched at high tension without rupture and can be used at a good condition for a long time.

Especially, when the core comprises polyester, the resultant screen gauze has excellent dimensional stability and thus enables precision printing without deformation when being stretched at high tension. When the core has an intrinsic viscosity of 0.60 or more, high strength at break can be obtained and the spinning workability can be stabilized. Especially, the sheath comprises nylon 6 having a relative viscosity of 2.0 or more, the monofilament can endure harsher abrasion in the weaving and thus is excellent in weaving performance, and also more precision printing can be realized.

Since the screen gauze of the present invention is formed by using the above-mentioned core-sheath composite monofilament for at least one of warp and weft, halation does not occur and thus clear printing pattern can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram illustrating one embodiment of the present invention.

FIG. 2 is a chart illustrating the relationship between colors of colorant or the like and reflectance.

BEST MODE FOR CARRYING OUT THE INVENTION

Now preferred embodiments of the present invention will be described below.

FIG. 1 shows a monofilament for use in a screen gauze according to an embodiment of the present invention. This monofilament comprises the core 1 and the sheath 2. The core 1 is formed by a fiber-forming polymer 4 containing a material 3 having a property of absorbing light at wavelengths of 350 nm to 450 nm.

When a photosensitive resin is cured by ultraviolet rays in producing a screen plate, light at wavelengths of 350 to 450 nm is generally irradiated. (However, the range for ultraviolet rays is up to 400 nm and light at wavelengths of 400 to 450 nm falls within a visible light range.) To prevent halation, it is necessary to suppress reflection in the range of 350 to 450 nm. Therefore, it is important to contain light absorbing material having a property of absorbing light within the above-mentioned range.

The light absorbing material 3 is not specifically limited as long as it has a property of absorbing light at wavelengths of 350 to 450 nm. Examples thereof include inorganic pigments such as talc, chromate salt, ferrocyanide, various metallic sulfate salts, sulfide, selenide and phosphate; organic pigments such as phthalocyanine, quinacridone, isoindolinone, perinone and dioxazine; azoic dyes such as benzene azos (monoazo or disazo), heterocyclic azos (thiazoleazo, benzothiazoleazo, quinolineazo, pyridine azo, imidazole azo or thiophene azo); dyes such as anthraquinone, indigoid condensation dyes (quinophthaline, styryl or coumarin), triphenylmethane dye, xanthene dye, alizarin dye, acridine dye or cyanine dye; carbon black, color fillers obtained by dispersing a pigment or a dye into particles formed by an organic compound. These are used either alone or in combination of two or more.

Among them, pigments or dyes are preferred in terms of heat resistance and dyes are optimum in terms of uniform dispersibility to the monofilament.

As the light absorbing material 3, preferred are those whose temperature for 1% weight reduction measured by means of differential thermogravimetric analysis (TG-DTA) is not less than 280° C. because physical properties such as filament strength or uneven yarn can easily be stabilized. Especially, those whose temperature is not less than 300° C. are more preferred. Further, preferred are those whose weight reduction in holding for ten minutes at 300° C. under nitrogen atmosphere is not more than 5% by weight because physical properties of the filament can easily be stabilized. Especially, those whose weight reduction is not more than 3% by weight are more preferred. It is easy to prevent deterioration of physical properties of the filament due to decomposition of the light absorbing material by decrease in melting viscosity during spinning within the above-mentioned range. Further, spinning workability is good.

The number average particle diameter of powders or particles used as the light absorbing material 3 is preferably 0.01 to 10 μm, more preferably, 0.05 to 2 μm. If the number average particle diameter is within this range, uneven yarn does not tend to occur. If the light absorbing material 3 is too large in its size, filament strength is deteriorated and thus uneven yarn tend to be caused because uniform dispersion of the light absorbing material 3 is difficult. If the light absorbing material 3 is too small in its size, it easily condenses and solidifies, and thus uneven yarn tend to be caused. Among them, a disperse dye hardly soluble to water is preferred in terms of spinning workability of polyester.

Typical examples of the disperse dye include DIANIX series available from DyStar Textilfarben GmbH & Co. Deutschland KG, SUMIKARON series available from Sumika Chemtex Company, Limited, KAYALON POLYESTER series, KAYALON MICROESTER series and KAYASET series all available from Nippon Kayaku Co., Ltd., MIKETON series and PALANIL series both available from Mitsui BASF Co., Ltd., TD series available from Daito Chemic Co., Ltd., KIWALON POLYESTER series available from Kiwa Chemical Industry Co., Ltd., TERASIL series available from Ciba Specialty Chemicals, FORON series available from Clariant and DIARESIN series available from Mitsubishi Kasei Hoechst, which are preferred. These are used either alone or in combination.

Preferable examples of commercially available yellowish dyes include DIARESIN YELLOW H2G available from Mitsubishi Kasei Hoechst, NYLOSAN YELLOW N-5GL available from OG Corporation. Preferable examples of commercially available reddish dyes include DIANIX Red AC-E available from DyStar Textilfarben GmbH & Co. Deutschland KG. Preferable examples of commercially available bluish dyes include DIANIX BLUE AC-E available from DyStar Textilfarben GmbH & Co. Deutschland KG.

It is known that dyes vary in light absorbing property depending on their colors. Core-sheath composite monofilaments were produced by using dyes in typical colors such as black (NYLOSAN Black F-ML available from OG Corporation), red (NYLOSAN RED F-RL200 available from OG Corporation), blue (NYLOSAN BLUE available from OG Corporation), yellow (NYLOSAN YELLOW N-5GL available from OG Corporation) and green (NYLOSAN GREEN F-BL available from OG Corporation) in accordance with the following Example 1 and each light absorbing property was measured by the following method. Each resultant reflectance is shown in FIG. 2. Similarly, a core-sheath composite monofilament (in white color) was produced by containing 1.0% by weight of titanium oxide into the core thereof and its reflectance was similarly determined. Further, reference numeral 11 indicates a light absorbing property in a black color, 12 for red color, 13 for blue color, 14 for yellow color, 15 for green color and 16 for white color, respectively, in FIG. 2.

Measuring Method of Light Absorbing Property

Each sample in a tubular shape was obtained by circular knitting monofilaments at the conditions of a wale number of 24/2.54 cm and a course number of 34/2.54 cm by means of a single-cylinder knitting machine (MODEL CR-B) manufactured by Koike Seisakusho and was folded twice for forming eight piles, and then was mounted on a measurement holder of 3 cm×3 cm. The reflectance in the wavelength range of 200 to 600 nm was measured in increments of 5 nm using a spectrophotometer UV-3101PC, manufactured by Shimadzu Corporation.

According to FIG. 2, it is found that red, yellow, green or black dye is suitable for use as the light absorbing material 3 of the present invention because the reflectance is low in the wavelength range of 350 to 450 nm.

Further, in the case where a dye is employed for the light absorbing material of the present invention, since it requires easiness to be seen when being adhered to a positive film in making a plate of a screen gauze, a yellowish or reddish dye is preferred. A yellowish dye is optimum because its reflectance is lower than a reddish dye in the above-mentioned wavelength range.

The monofilament of the present invention has preferably average reflectance of 15% or less to light at wavelengths of 350 nm to 450 nm, more preferably 10% or less, and most preferably 8% or less. Since light having such wavelengths is mainly reflected when a photosensitive resin is cured with ultraviolet rays in making a plate, it is preferred to suppress reflection of light having such wavelengths to prevent halation. When the average reflectance in this wavelength range is within the above-mentioned range, halation does not tend to occur on surfaces of warps or wefts, undesired portion will not be exposed to light for curing and thus precision printing can be realized.

As the fiber-forming polymer 4 containing the light absorbing material 3, any polymer is acceptable as long as it has been conventionally used for manufacturing a monofilament. Examples thereof include polyolefins such as polyethylene or polypropylene, modified polyolefins composed mainly thereof, polyamides such as nylon 6, nylon 66, nylon 10 or nylon 12, modified polyamide copolymers composed mainly thereof, polyesters such as polyethylene terephthalate (just referred as PET, hereinafter), polybutylene terephthalate, polytetraethylene terephthalate or polyethylene naphthalate, aliphatic polyesters such as polylactic acid or polyglycolic acid, modified polyester copolymers composed mainly thereof, polyalylate, polybenzazole, all aromatic polyesters, all aromatic polyamides. Among them, polyesters are preferred in terms of their dimensional stability and strength.

The proportion of the light-absorbing material 3 to the fiber-forming polymer 4 depends on kinds of the light-absorbing material 3 or the cross-sectional area ratio between the core and the sheath, which is, however, usually 0.1 to 2.0% by weight, preferably 0.3 to 2.0% by weight, most preferably 0.3 to 1.0% by weight based on the total core. When the proportion is within this range, halation can effectively be prevented. Also, since the reduction in melting viscosity can be suppressed, spinning workability is good. When the proportion is too large, the resultant monofilament goes brittle and may not be stretched at high tension.

The proportion of the light absorbing material is usually 0.1 to 1.8% by weight, preferably 0.4 to 1.4% by weight, most preferably 0.3 to 0.7% by weight based on the total filament in terms of effectiveness.

The sheath 2 (return to FIG. 1) does not contain the light absorbing material 3 and is formed by suitable fiber-forming polymer 5. As the fiber-forming polymer 5, any polymer is acceptable as long as it has been conventionally used for manufacturing a monofilament as same as the fiber-forming polymer used for the above-mentioned core 1. Examples thereof include polyolefins such as polyethylene or polypropylene; modified polyolefins composed mainly thereof; polyamides such as nylon 6, nylon 66, nylon 10 or nylon 12; modified polyamide copolymers composed mainly thereof; polyesters such as polyethylene terephthalate, polybutylene terephthalate or polytetraethylene terephthalate; and modified polyester copolymer composed mainly thereof. Among them, polyamides are preferred because the scraping of the filament surface is reduced.

As the fiber-forming polymer 5 of the sheath 2, those which do not contain the light absorbing material are exemplified herein. However, as long as the effects of the present invention are not deteriorated, the sheath may contain a small amount of the light absorbing material. When the sheath contains the light absorbing material, it is preferred that weight ratio of the light absorbing material in the core is larger than that in the sheath. As shown in FIG. 1, as the fiber-forming polymer 5 of the sheath 2, those which do not contain the light absorbing material are more preferred. Especially, the light absorbing material having large diameter (for example, 1 μm or more) of the dye or the particles may preferably not be contained to prevent deterioration of weaving performance due to the scraping of the reed, or maintain good filament physical properties such as strength and good spinning workability.

As fiber forming polymers for the core 1 and the sheath 2, the above-mentioned polymers may be used. Especially, the preferable combination is as follows. As the fiber forming polymer 4 of the core 1 is preferably polyester having an intrinsic viscosity of 0.60 or more, because such polyester has sufficient filament strength to be stretched at high tension and thus precision printing can easily be realized. As the fiber forming polymer 5 of the sheath 2, nylon 6 having relative viscosity of 2.0 or more is preferred, because such nylon has sufficient filament strength to be stretched at even higher tension.

The cross-sectional area ratio of the core 1 to the sheath 2 is not specifically limited, as long as the core sheath composite monofilament can be spun. However, the cross-sectional area ratio is typically core:sheath=40:60 to 90:10, preferably 40:60 to 70:30. If the cross-sectional area ratio of the core 1 is lower than the range described above, the light absorbing effect hardly develops, which may cause halation, whereas if it is higher than the range described above, spinning work ability may be deteriorated or printing capability may be deteriorated due to uneven yarn. Therefore, when such a ratio is within the above-mentioned range, halation can effectively be restrained, spinning workability can be stabilized and thus uneven yarn can be reduced, and the sheath works effectively to protect the core so as to endure harsh abrasion in the weaving of the high mesh screen or printing. As a result, precision printing can easily be obtained.

The fineness of the monofilament of the present invention can appropriately be determined depending on the size of the screen gauze, required resolution or the like. The fineness of the monofilament is typically 4 to 30 dtex, preferably 7 to 18 dtex. When the fineness is finer than 4 dtex, the monofilament may not be woven. When the fineness is thicker than 30 dtex, spinning workability may be deteriorated and close high mesh structure cannot be formed, which may impair the aim of the present invention that high image quality can be obtained. When the fineness is within the above-mentioned range, spinning workability can be stabilized and close high mesh structure can be obtained, so that clear image can be obtained in screen printing.

Further, the core-sheath composite monofilament preferably has an elongation at break of 20 to 30% and strength at break of 5.5 cN/dtex or more, more preferably 5.7 cN/dtex or more, for use in a screen gauze. When the elongation at break is within the range of 20 to 30%, weaving performance is good. Also, when the strength at break at that time is 5.5 cN/dtex or more, the screen gauze can be stretched at high tension, resulting in more precise printing.

Further, the core and/or the sheath of the monofilament in this invention may be blended with inorganic particles so as to improve spinning workability to the extent that the average reflectance of the monofilament is not extremely aggravated. Examples thereof include titanium oxide, zinc oxide, magnesium carbonate, silicon oxide, calcium carbonate and alumina. The inorganic particles are not specifically limited as long as they do not affect spinning workability. However, titanium oxide is preferred in terms of dispersibility and cost performance. Further, the inorganic particles may preferably be added at 0.1% by weight or more based on the whole filament to improve spinning workability, more preferably at 0.3% by weight or more. However, when the inorganic particles are added too much, the average reflectance of the monofilament is insufficient or abrasion resistance to reed at high mesh weaving may be deteriorated. Therefore, the upper limit thereof is preferably 1% by weight, more preferably 0.5% by weight. When the amount thereof is within the above-mentioned range, it is easy to satisfy the two features of spinning workability of the monofilament and abrasion resistance at high mesh weaving.

The average diameter of the inorganic particles is preferably 0.01 to 2 μm, more preferably 0.05 to 1 μm. When the diameter is within this range, dispersibility of the particles is good and thus uneven yarn does not tend to occur, resulting in stable strength.

The core-sheath composite monofilament of the present invention may, for example, be produced in the following manner. First, fiber-forming polymer pellets such as polyester for forming the core are dried in vacuum and put into a mixing means such as a twin screw kneader. A light absorbing material such as yellow dye is put into the mixing means so as to be within a specified ratio. Both of them are sufficiently kneaded and then extruded, and thus the kneaded pellets are obtained. On the other hand, fiber-forming polymer pellets, such as polyamide for forming the sheath, are prepared by drying in vacuum in the same manner as in the core. The intended core-sheath composite monofilament can be obtained by melt-spinning the thus obtained two kinds of pellets by means of a specific spinneret in accordance with the conventional melt-spinning method.

When polyester polymer pellets are used for forming the core, moisture content of 20 ppm or less (corresponding to 20 mg/kg or less) is preferable for kneading. When polyamide polymer pellets such as nylon 6 are used for forming the sheath, moisture content of 100 ppm or less (corresponding to 100 mg/kg or less) is preferred. In this way, when pellets having such moisture content as not exceeding a specific level are used, spinning workability can be further improved.

It is preferred that the melting viscosity of fiber-forming polymer pellets for forming the core is higher than the usual level to sufficiently increase the strength of the resultant core-sheath composite monofilament. For example, the intrinsic viscosity is preferably 0.60 to 0.80.

In the case where the light absorbing material and the fiber forming polymer are kneaded in the twin screw kneader or the like, it is preferred that such materials will not absorb moisture as less as possible during the process. The rapid viscosity reduction of kneaded pellets can be restrained, so that pellets suitable for effective spinning workability can be obtained. To restrain moisture absorption, it is preferred that a pellet supply tank is arranged to be under nitrogen atmosphere when supplying pellets to a kneader, or the light absorbing material and the fiber forming polymer are kneaded and extruded with vacuuming at 80 kPa or less.

As the fiber forming polymer for the core, various polymers are acceptable, as described above, however, polyesters are preferred. This is because dimensional stability is excellent, which is necessary for stretching a high mesh screen at high tension and thus precision printing is realized. Especially, PET is more preferred in terms of cost performance and spinning workability. When the core comprises polyester, the intrinsic viscosity of the kneaded pellets is preferably 0.60 or more, more preferably 0.62 or more. When the intrinsic viscosity is 0.60 or more, higher strength at break can be realized, and thus the resultant screen gauze can be stretched at high tension. Further, since the melting viscosity is maintained at high level in spinning, spinning workability is good. The upper limit of the intrinsic viscosity is not specifically limited, however, a value of 0.90 is sufficient in terms of stable workability of melt spinning.

As the fiber forming polymer for the sheath, various polymers are acceptable, as described above, however, polyamides are preferred. Especially, nylon 6 is preferred. When the sheath comprises nylon 6 having relative viscosity of 2.0 or more, higher strength at break can be realized, and thus the resultant screen gauze can be stretched at high tension. The upper limit of the relative viscosity is not specifically limited, however, a value of 3.5 is sufficient in terms of stable workability of melt spinning.

The screen gauze of the present invention can be obtained by weaving and stretching the thus obtained core-sheath composite monofilament according to the conventional method. The weaving conditions are not specifically limited. The thus obtained monofilament can be used for either warps or wefts, or both warps and wefts. In the case of the usual high mesh screen gauze, if the core-sheath composite monofilament is used for either warps or wefts, sufficient capability can be exerted, which is lower cost than the case where the core-sheath composite monofilament is used for both warps and wefts. Since halation can be further lowered in the case where the core-sheath composite monofilament is used for both warps and wefts, the resultant screen gauze can preferably be used for more precise printing.

Since the core-sheath composite monofilament makes high precision printing easy, a high mesh screen gauze of 300 mesh or more is preferred, and that of 400 mesh or more is more preferred.

Although the resultant screen gauze can be obtained at low cost, it shows good light absorbing property that average reflectance is 15% or less to light at wavelengths of 350 nm to 450 nm, and does not cause halation, and enables good ink-release, and thus can form clear printing pattern. Especially, the average reflectance of 10% or less to light at wavelengths of 350 nm to 450 nm is preferred in terms of prevention of halation.

EXAMPLES

Examples of the present invention will be described below in conjunction with Comparative Examples. Also, the measuring methods and the evaluation methods of each property are as follows.

Intrinsic Viscosity and Relative Viscosity

Each viscosity was measured by automatic viscosity measurement equipment (SS-600-L1 model available from Shibayama Scientific Co., Ltd.). The intrinsic viscosity was measured using phenol/tetrachloroethane (volume ratio: 6/4) as solvent at constant-temperature bath of 20° C. The relative viscosity was measured using 96% concentrated sulfuric acid as solvent so as to be sample concentration of 1 g/dL at constant-temperature bath of 25° C.

Spinning Workability

Each monofilament was continuously spun for one day using an actual spinning machine. Each extrusion stability and yield of the core polymer and the sheath polymer, and each shape stability of the core-sheath shape were observed and evaluated. The symbol ⊚ indicates that all items were stabilized and very good, the symbol ◯ indicates that all items were almost stabilized and good, and the symbol × indicates that any item was poor.

Strength at Break and Elongation at Break

In accordance with JIS L 1013, using an AGS-1KNG autograph tensile tester manufactured by Shimadzu Corporation, strength at break and elongation at break are determined under the conditions at a specimen yarn length of 20 cm and a constant tensile speed of 20 cm/min.

Average Reflectance

A sample in a tubular shape was obtained by circular knitting each monofilament at conditions of a wale number of 24/2.54 cm and a course number of 34/2.54 cm by means of a single-cylinder knitting machine (MODEL CR-B) manufactured by Koike Seisakusho and was folded twice for forming eight piles, and then was mounted on a measurement holder of 3 cm×3 cm. The reflectance in the wavelength range of 350 to 450 nm was measured in increments of 5 nm using a spectrophotometer UV-3101PC, manufactured by Shimadzu Corporation, and then average reflectance was determined.

Weaving Performance

A 300 mesh screen gauze was woven using each core-sheath composite monofilament by a Sluicer type weaving machine (G-6200) to observe each frequency of yarn breakage and scam occurrence and evaluate thereof. A woven length was measured when weaving could no more be conducted normally and the weaving machine had to be stopped. The symbol ⊚ indicates excellent when the woven length was 1000 m or more, the symbol ◯ indicates good when the woven length was 500 m or more and the symbol × indicates poor when it was less than 500 m.

Tensioning Performance

Each 300 mesh screen gauze was stretched over a frame at a tension of 35 N on the bias of 22.5° and then whether the screen gauze would be disrupted was observed. The symbol × indicates poor tensioning when the screen was disrupted, the symbol Δ indicates slightly good when the screen was not disrupted at a tension of 35 N, but disrupted at a tension of 40 N, the symbol ◯ indicates good when the screen was not disrupted at a tension of 40 N, but disrupted at a tension of 45 N, and the symbol ⊚ indicates excellent when the screen was not ruptured at a tension of 45 N.

Printing Capability

A photosensitive diazo resin was coated with a thickness of 10 to 11 μm on a 300 mesh screen gauze stretched over a frame of 320 mm×205 mm at a tension of 35 N and was covered with a photomask having a striped pattern having a width of 400 μm and a pitch of 400 μm. A screen gauze coated and stretched in the same manner as above was covered with a photomask having a striped pattern having a width of 200 μm and a pitch of 200 μm. Thereafter, the thus obtained samples were optically exposed appropriately and were washed with water for obtaining two kinds of printing plates. Then, each 100 pieces were consecutively printed using the printing plates. The printed images and lines were photographed at a 400-power microscope and observed. If halation occurred, curing of the photosensitive resin was distorted, lines of the striped pattern were uneven or thick and thin parts were caused. Therefore, each evaluation was conducted in the following manners.

-   Excellent (⊚): Even striped pattern and no thick and thin part. -   Good (◯): Curing of a photosensitive resin was distorted and     unevenness or thick and thin parts slightly occurred on striped     patterns or occurred in a few pieces. -   Poor (×): Curing of a photosensitive resin was distorted and     remarkable unevenness or thick and thin parts occurred. -   Impossible (−): Printing capability could not be evaluated because     the screen gauze was ruptured when being stretched.

EXAMPLE 1

Homo PET (polyester) pellets having an intrinsic viscosity of 0.66 were dried in vacuum until the pellet moisture became 20 ppm (20 mg/kg) in accordance with Karl Fischer moisture measurement method. The resultant product was put into a twin screw kneader under a nitrogen purge and then yellow dye (DIARESIN YELLOW H2G DISPERSE YELLOW 160 available from Mitsubishi Kasei Hoechst) was kneaded therein so as to be 1.0% by weight. Such kneading and extrusion was conducted with vacuuming at 80 kPa. The intrinsic viscosity of the kneaded product was 0.64.

The thus obtained PET pellets containing yellow dye were used as the core ingredient and semi-dull nylon 6 pellets (content of titanium oxide: 0.4% by weight, relative viscosity: 2.6) similarly prepared by drying in vacuum until the pellet moisture became 100 ppm (100 mg/kg) were used as the sheath ingredient. An undrawn composite monofilament having a core-sheath cross-sectional ratio of 50:50 was obtained by using a spinneret for melt-spinning a core-sheath composite monofilament. The resultant undrawn monofilament was drawn under the conditions of a roller heater at 85° C., a plate heater at 150° C. and a draw ratio specifically arranged to obtain a core-sheath composite monofilament of 13 dtex having an elongation at break of 25%±1%.

EXAMPLES 2 TO 5 AND COMPARATIVE EXAMPLES 1 AND 2

The core-sheath composite monofilament was obtained in the same manner as in the Example 1 except that the content of each yellow dye in the core was changed as shown in the following Table 1.

Each core-sheath monofilament was measured and evaluated in terms of spinning workability, average reflectance in the wavelength range of 350 to 450 nm, strength at break, weaving performance, tensioning performance and printing capability in accordance with the above-mentioned manner. These results are also shown in the following Table 1.

TABLE 1 Comparative Example example 1 2 3 4 5 1 2 Content of yellow dye in the 1.0 0.1 0.3 2.0 3.0 —  0.07 core (% by weight) Evaluation Spinning workability ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ Average reflectance (%) 4.9 14.8  11.1  4.3 4.0 48.7  15.2  Strength at break (cN/dtex) 5.8 6.3 6.1 5.5 5.2 6.4 6.2 Weaving performance ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ ⊚ Tensioning performance ⊚ ⊚ ⊚ ◯ Δ ⊚ ⊚ Printing capability 400 μm pitch ⊚ ◯ ⊚ ⊚ ◯ X X 200 μm pitch ⊚ ◯ ⊚ ⊚ ◯ X X

Since the yellow dye was not contained at all in the Comparative Example 1, the average reflectance was high, causing halation in the evaluation of printing capability, which was poor performance. Since the average reflectance was insufficient in the Comparative Example 2, halation was caused as same as in the Comparative Example 1, which was poor printing performance. On the other hand, the Examples 1 to 5 according to the present invention were good at all of weaving performance, tensioning performance and printing capability. Especially, since the content of each yellow dye in the core in the Examples 1 and 3 was optimum, the Examples 1 and 3 had excellent results in all properties.

Various Evaluations Due to Difference in Manners of Containing Light Absorbing Material COMPARATIVE EXAMPLE 3

Nylon 6 pellets having a relative viscosity of 2.5 were dried in vacuum until the pellet moisture became 500 ppm (500 mg/kg) in accordance with Karl Fischer moisture measurement method. The resultant product was put into a twin screw kneader under a nitrogen purge and then yellow dye (DIARESIN YELLOW H2G DISPERSE YELLOW 160 available from Mitsubishi Kasei Hoechst) was kneaded therein so as to be 1.0% by weight. Such kneading and extrusion was conducted with vacuuming at 80 kPa. The relative viscosity of the kneaded product was 2.6.

The thus obtained nylon 6 pellets containing yellow dye was used as the sheath ingredient and PET not containing the yellow dye and having an intrinsic viscosity of 0.66 was used as the core ingredient. A composite monofilament having a core-sheath cross-sectional ratio of 50:50 and having fineness of 13 dtex was spun by using a spinneret for a melt-spinning a core-sheath composite monofilament.

COMPARATIVE EXAMPLE 4

A monofilament having a circular cross section instead of a core-sheath type and having fineness of 13 dtex was spun using nylon 6 pellets containing yellow dye as same as in the Comparative Example 2.

EXAMPLES 6 AND 7

A core-sheath composite monofilament was produced as Example 6 in the same manner as in the Example 1 except that red dye (DIANIX RED AC-E available from DyStar Textilfarben GmbH & Co. Deutschland KG) was used instead of the yellow dye. A core-sheath composite monofilament was produced as Example 7 in the same manner as in the Example 1 except that green dye (NYLOSAN GREEN F-BL available from OG CORPORATION) was used instead of the yellow dye.

Each monofilament was measured or evaluated in terms of spinning workability, average reflectance, strength at break, weaving performance, tensioning performance and printing capability. These results are also shown in the following Table 2.

Since the sheath ingredient contained the yellow dye in the Comparative Example 3, scum occurred by the scraping of reed during weaving and thus weaving performance was bad. Since the yellow dye was contained in the whole monofilament of the Comparative Example 4, melt viscosity was drastically deteriorated and thus spinning workability was bad. Further, the Comparative Example 4 was bad in weaving performance as same as in the Comparative Example 3, and further stretching was also difficult. On the other hand, the Example 6 and the Example 7 in accordance with the present invention were excellent at spinning workability and weaving performance.

Various Evaluations Due to Difference in Core to Sheath Cross-Sectional Area Ratio EXAMPLES 8 TO 12

A core-sheath composite monofilament was produced in the same manner as in the Example 1 except that the core to sheath cross-sectional area ratio was changed as shown in the following Table 3. Each core-sheath composite monofilament was measured or evaluated in terms of spinning workability, average reflectance, strength at break, weaving performance, tensioning performance and printing capability. These results are also shown in the following Table 3.

TABLE 3 Example 8 9 10 11 12 Core-sheath cross-sectional area 30:70 40:60 70:30 90:10 95:5 ratio (core:sheath) Content of dye based on total 0.3 0.4 0.7 0.9  0.95 filament (% by weight) Evaluation Spinning workability ⊚ ⊚ ⊚ ◯ ◯ Average reflectance (%) 10.7  5.8 4.8 4.4 4.3 Strength at break (cN/dtex) 6.1 5.9 5.7 5.5 5.4 Weaving performance ⊚ ⊚ ⊚ ⊚ ◯ Tensioning performance ⊚ ⊚ ⊚ ◯ Δ Printing capability 400 μm pitch ◯ ⊚ ⊚ ⊚ ⊚ 200 μm pitch ◯ ⊚ ⊚ ◯ ◯

Since the ratio of the core was relatively low in the Example 8, the average reflectance was slightly high and thus the printing capability remained good. Since the strength at break was slightly low in the Example 11, the tensioning performance remained as good. As a result, the Example 11 could not be stretched at high tension, the printing capability remained as good only at 200 μm pitch. Since the protecting layer is too few in the Example 12, the tensioning performance remained as slightly good. On the other hand, the core-sheath cross-sectional area ratio was optimum respectively each in the Example 9 and the Example 10, all evaluations were excellent.

Various Evaluations Due to Difference in Intrinsic Viscosity of Polyester as the Core Ingredient EXAMPLES 13 TO 15

Each kneaded PET varied in intrinsic viscosity was obtained in the same manner as in the Example 1 except that the intrinsic viscosity of the homo PET was changed. The core-sheath composite monofilament was produced in accordance with the manner mentioned in the Example 1 except that the thus obtained PET was used, and then the screen gauze was evaluated. The intrinsic viscosity of each kneaded PET, the intrinsic viscosity of each core ingredient, the strength at break and the tensioning performance of each screen gauze are shown in the following Table 4.

TABLE 4 Example 13 14 1 15 Intrinsic viscosity of kneaded PET 0.60 0.62 0.64 0.75 Intrinsic viscosity of core ingredient 0.58 0.60 0.62 0.72 Strength at break (cN/dtex) 5.7 5.9 6.0 6.5 Tensioning performance ◯ ⊚ ⊚ ⊚

Since the intrinsic viscosity was slightly low in the Example 13, the strength at break did not reach an excellent level and thus the tensioning performance remained as good. Since each value of the strength at break of the Examples 1, 14 and 15 was higher, each tensioning performance was excellent.

Various Evaluations Due to Difference in Relative Viscosity of Nylon 6 as Sheath Ingredient EXAMPLES 16 TO 18

Each core-sheath composite monofilament was obtained in the same manner as in the Example 1 except that the relative viscosity of nylon 6 as the sheath ingredient was changed variously. Each of the thus obtained screen gauze was evaluated and the results are shown in the following Table 5.

TABLE 5 Example 16 17 1 18 Relative viscosity 1.8 2.0 2.6 3.3 Strength at break (cN/dtex) 5.5 5.8 6.0 6.4 Weaving performance ◯ ⊚ ⊚ ⊚ Tensioning performance ◯ ⊚ ⊚ ⊚

Since the relative viscosity was slightly low in the Example 16, the strength at break did not reach an excellent level and thus the weaving performance and the tensioning performance each remained as good. Since each value of the strength at break of the Examples 1, 17 and 18 was higher, each tensioning performance was excellent. Further, since nylon 6 fulfilled sufficiently the role of the protecting layer of the core ingredient, scum did not occur by abrasion of reed during weaving.

COMPARATIVE EXAMPLE 5

The core-sheath composite monofilament was obtained in the same manner as in the Example 1, except that homo PET pellets having intrinsic viscosity of 0.66 were used as the core ingredient. The thus obtained monofilament was circular-knitted. The thus obtained circular-knit was dipped in dyeing solution to which 1.0% by weight of yellow dye (NYLOSAN YELLOW N-5GL available from OG CORPORATION) and 1% by weight of ammonium sulfate based on the total weight of the circular-knit were added. The solution was heated to a boil with stirring for 30 minutes so that the dye was adsorbed at 0.5% by weight. Thereafter, the solution was maintained at 95° C. for 25 minutes. Then, the circular-knit was taken out of the dying solution, and washed in water, and then allowed to dry naturally. The weight of the circular-knit was increased by 0.5% by weight after being dyed.

The dyed circular-knit was raveled and the strength at break of the thus obtained monofilament was measured in the same manner as above. The value thereof was 5.0 cN/dtex. The average reflectance of the thus obtained monofilament was measured in the same manner as above. The value thereof was 6.2%. Further, a 300 mesh screen gauze was woven by using the thus obtained monofilament, and was tried to be stretched over a screen frame at a tension of 35 N, and, however, was ruptured due to insufficient strength of the monofilament.

EXAMPLE 19

A 300 mesh screen gauze was woven by using the core-sheath composite monofilament obtained in the Example 1 as warps and the homo PET monofilament having fineness of 13 dtex as wefts by a Sluicer type weaving machine (G-6200). The thus obtained screen gauze was stretched over a screen frame at a tension of 35 N on the bias of 22.5°. The printing capability was evaluated in the same manner as in the Example 1. As a result, thick and thin parts were slightly caused in the striped pattern due to halation, which was a fairly small amount and was also caused infrequently, and thus the printing capability was good (◯).

EXAMPLE 20

The screen gauze was obtained and the printing capability was evaluated in the same manner as in the Example 19, except that the homo PET monofilament having fineness of 13 dtex was used as warps and the core-sheath monofilament obtained by the Example 1 was used as wefts. As a result, thick and thin parts were slightly caused in the striped pattern due to halation, which was a fairly small amount and was also caused infrequently, and thus the printing capability was good (◯), as same as in the Example 19.

INDUSTRIAL APPLICABILITY

As described above, the monofilament of the present invention is suitable for use in the screen gauze which requires printing capabilities such as high precision and good working efficiency. Especially, the monofilament of the present invention is effective for a high-mesh screen gauze having 300 mesh or more. 

1. A screen gauze, characterized in that at least one of warp and weft of said screen gauze comprises a core-sheath composite monofilament, said core-sheath composite monofilament comprising: a core formed by a fiber-forming polymer containing a light-absorbing material having a property of absorbing light at wavelengths of 350 nm to 450 nm, and a sheath formed by a fiber-forming polymer, said core-sheath composite monofilament having average reflectance of 15% or less to light at wavelengths of 350 nm to 450 nm.
 2. The screen gauze of claim 1, wherein said light-absorbing material is present in an amount of 0.1 to 2.0% by weight based on the total core.
 3. The screen gauze of claim 1, wherein the cross-sectional area ratio of core to sheath is in a range of 40:60 to 90:10.
 4. The screen gauze of claim 1, wherein the elongation at break of said core-sheath composite monofilament is 20 to 30% and the strength at break of said core-sheath composite monofilament is 5.5 cN/dtex or more.
 5. The screen gauze of claim 1, wherein said core comprises polyester having an intrinsic viscosity of 0.60 or more.
 6. The screen gauze of claim 1, wherein said sheath comprises nylon 6 having a relative viscosity of 2.0 or more. 